Recovery of fluorene, dibenzofuran and acenaphthene from coal hydrogenation neutral middle oil



April 24, l962 D. c. ovERHoLT ET Al.

RECOVERY OF FLUORENE FROM COAL HYDROGENATION NEUTRAL MIDDLE OIL Filed Sept. 10, 1958 Unite In the hydrogenation of coal the product is ordinarily separated into several product mixtures, one Vof which is designated neutral middle oil. This neutral middle oil is composed of a mixture of aromatic hydrocarbon compounds having boiling temperatures between about 265 and 320 C., the acidic and basic components such as phenolics, nitrogen bases and indoles having been removed. The major components of the neutral middle oil are ordinarily iluorene, acenaphthene, dibenzofuran, methyl-substituted fluorenes, and various homologues of naphthalene, including mono, diand trimethylnaphthalines. These compounds contain from about ll to about 16 carbon atoms and have molecular weights from about 130 to about 190.

f Individual compounds in the neutral middle oil seldom occur in concentrations higher than about 5 percent by weight of the total. In the boiling temperature range of 265 C. to 320 C. the boiling temperatures of individual compounds are quite close to one another and this fact, coupled with the low concentrations of individual compounds, make separation of the compounds quite diliicult. Separation by ordinary distillation has proved economically impractical and in some cases it is actually impossible due to the closeness of the boiling points.

A known method of recovering fluorene from such mixtures is by fusing with potassium hydroxide at a temperature of about 300 C. to form the potassium salt of lluorene. This salt can then be reacted with water to regenerate fluorene and potassium hydroxide. This process is by its nature a batch operation, requires high temperatures with expensive heat exchange equipment and is limited to recovering fluorene.

We have now discovered a low temeprature process for continuously recovering simultaneously from coal hydrogenation neutral middle oil, as separate products, fluorene, dibenzofuran and acenaphthene. Our, process is based upon our discovery that lower alkylene glycols, particularly diethyleneA glycol, are selective `solvents for uorene, dibenzofuran and acenaphthene. Furthermore, we discovered that such glycols will extract these three compounds from naphthalene homologs and other aromatic hydrocarbons present in the mixture.

According to the process of our invention therefore, the coal hydrogenation neutral middle oil is first extracted with a lower alkylene glycol, for example, diethylene glycol, to remove as extract a mixture of liuorene, dibenzofuran and acenaphthene. If desired, the extract can be scrubbed with a naphtha or aliphatic hydrocarbon to remove any unwanted aromatic hydrocarbons which may have been extracted; this scrubbing can be accomplished as a concurrent extraction at the time ofthe glycol extraction. Recovery of the lluorene-dibenzofuran-acenaphthene mixture from the glycol extract thereof is \.mplished by a back-extraction with isopropyl ether m aliphatic hydrocarbon such as n-heptane. If desired this new extract can be water-washed to remove traces of the glycol solvent. Distillation can then be employed to recover iluorene, dibenzfuran and acenaphthene. If desired, these compounds can be further rened -by recrystallization from an appropriate solvent, for example isopropanoLA rarest tem C 3,031,463 Patented Apr. 24, A1962 Wey demonstrated the workability of our process by determining the distribution coecients of uorene, dibenzofuran and acenaphthene between diethylene glycol and n-heptane. This was done by dissolving a weighed portion of one of the compounds, either lluorene, dibenzouran or acenaphthene, in a known weight of n-heptane, and then equilibrating the solution thus formed with an equal weight of diethylene glycol. The phases were then separated and the n-heptane phase was analyzed gravimetrically for the compound under consideration. The distribution coefficients were then calculated as the concentration of the compound in the diethylene glycol extract divided by the concentration of the compound in nheptane. Fluorene was found to have a distribution coeilcient between diethylene glycol and n-heptane of 0.19, dibenzofuran to have one of 0.35 and acenaphthene one of 0.25.

The workability of scrubbing the glycol extract of fluorene, dibenzofuran and acenaphthene with a naphtha or aliphatic hydrocarbon to remove undesirable aromatios was demonstrated in a similar manner. Distribution coefficients between diethylene glycol and n-heptane that is, the concentration of the compound in n-heptane dividedv by the concentration of the compound in diethylene glycol, were determined to be 5.3 for uorene, 2.7 for dibenzofuran, 4.0 for acenaphthene and 20 for the other hydrocarbons in neutral ntiddle oil. In a similar manner the workability of back-extracting lluorene, dibenzofuran and acenaphthene from the glycol using isopropyl ether or an aliphatic hydrocarbon was demonstrated. Distribution coeicients between isopropyl ether and diethylene glycol, that is, the concentration of the compound in isopropyl ether divided by the concentration of the compound in diethylene glycol, were determined to be 5.2 for uorene, 4.1 for dibenzofuran and 4.5 for acenaphthene.

A preferred embodiment of the invention is shown in the ilow diagram of the drawing. In this embodiment neutral middle oil is extracted with diethylene glycol and the diethylene glycol extract containing norene, dibenzofuran and acenaphthene is scrubbed with heptane to remove undesirable aromatic hydrocarbons. The diethylene glycol extract is then back-extracted with isopropyl ether and the ether extract of these three compounds is iirst washed with water to remove any traces of diethylene glycol after which the ether is removed by vaporizing it from the mixture. The mixture is then fractionally distilled and each of the individual components is separately distilled and then recrystallized from isopropanol.

ln the drawing the ow diagram depicts a compound extraction column 11 for the primary extraction with the glycol and the scrubbing with heptane, an extraction column 12 for back-extracting with ether, a Washing column 13 for Water-washing the ether extract and a still 14 for removing the ether. Also shown are a still 15 for fractional distillation of the acenaphthene, dibenzofuran and fluorene, and crystallizers 16, 17 and 18 for final recovery of each of these three compounds.

. The neutral middle oil feed is introduced into extraction column 11 through line 19, while simultaneously diethylene glycol in line 20 and n-heptane in line 21 are introduced into column 11 whereby the feed is extracted with the glycol and back-extracted or scrubbed withk tion column 11 in line 22 into extraction column 12.y

The heptane solution of the remaining aromatic hydrocarbons from the middle oil, which constitute the bulk of those other than fluorene, dibenzofuran and acenaphthene, are removed from extraction column 11 through line 23 for recovery of the hydrocarbons. Isopropyl ether is introduced into extraction column 12 through line 24 and serves to back-extract the luorene, dibenzofuran and acenaphthene from the-glycol. The diethylene glycol is removed from extraction column 12 through line 25 and after removal any ether present in it can be recycled for reuse in the process. The ether extract of fluorene, dibenzofuran and acenaphthene, togetherwith residual traces of the glycol, is removed from extraction column 12 through line 26 and conveyed therein to the washing column 13. Water is introduced through line 27 into the washing column 13 where it Washes the traces of glycol from the ether extract. The wash water and traces of glycol are removed from washing column 13 through line 2S and discarded.

The ether extract of iluorene, dibenzofuran and acenaphthene is removed from washing column 13 through line 29 and conveyed therein to still 14 wherein the ether is vapor-ized and removed through line 30 for recovery and recycle to the process. The uorene, dibenzofuran and acenaphthene are removed from still 14 through line 31 and conveyed therein to still 15. In still 15 the mixture of uorene, dibenzofuran and acenaphthene is fractionally distilled. The acenaphthene vaporizes rst and is removed from still through line 32 and conveyed therein to line 33 wherein it is conveyed into crystallizer 16. Isopropanol is introduced into crystallizer 16 through line 34 and recrystallized acenaphthene product is removed frorn crystallizer 16 through line 35. After vaporization of acenaphthene in the still 15 the dibenzofuran is vaporized and removed from still 15 through line 32 and conveyed therein to line 36 wherein it is conveyed into crystallizer 17. Isopropanol is introduced into crystallizer 17 through line 37 and recrystallized dibenzofuran product is removed from crystallizer 17 through line 38. After vaporization of dibenzofuran in the still 15 the tluorene is vaporized and removed from still 15 through line 32 and conveyed therein into crystallizer 18. Isopropanol is introduced into crystallizer 1S through line 39 and recrystallized fluorene product is removed from crystallizer 18 through line 40.

In the preferred embodiment of the invention depicted in the flow sheet the extraction column 11 is a columnar liquid-liquid contacting device with internal reflux, such that the glycol extraction and naphtha scrubbing are conducted simultaneously. It may be a pulse column, a rotating disc contactor, a spray column, a baied column or a column packed with Raschig rings or the like. The glycol enters near the top of the column as the .continuous phase, the naphtha such as n-heptane back-extracts the undesirable aromatics by flowing upward counter-current to the diethylene glycol extract in the lower part of the column or scrubbing section. The nap-htha then dilutes the neutral middle oil at the middle oil feed plate to provide the necessary difference in specific gravities between the glycol and oil phases and to reduce the viscosity of the neutral middle oil. The naphtha-middle oil phase ows upward into the top section of the column or extraction section where the extraction of the fluorene, dibenzofuran and acenaphthene occurs. If desired, separate columns could be used for the glycol extraction and naphtha scrubbing operations. This, however, would require external reilux of the aromatic hydrocarbons scrubbed from the diethylene glycol extract.

The extraction of the neutral middle oil with diethylene glycol and the scrubbing with a naphtha are preferably conducted at a temperature of about 70 C. in order to take advantage of the lower viscosity of diethylene glycol at this temperature. When the naphtha is n-heptane temperaturesto about 79 C. may be employed but this temperature shouldnot be exceeded because of -the -possibility of gasification and n-heptane-water azeotro-pe formation. If operation at a higher temperature is desired higher boiling hydrocarbons such as octane, nonane and the like could be used. All of the compounds in the neutral middle oil feed to the process have boiling temperatures above 250 C. Lower boiling hydrocarbons such as pentane and hexane can be employed if lower temperatures are maintained in the extraction column. Temperatures as low as 35 C. can be employed. From 24 to 30 volumes of diethylene glycol per volume of neutral middle oil can be employed, with about 24 volumes of glycol per volume of oil preferred. 'Ihe volume of naptha used can be from 5 to 6 volumes of naptha per volume of neutral middle oil, with about 5 volumes of naptha per volume of oil preferred.

The back-extraction of the diethylene glycol extract with a secondary solvent such as isopropyl ether or other suitable compounds is conducted at a temperature of from 40 C. to 60 C. with about 50 C. preferred. The volume ratio of ether to glycol extract can be between 1:2 and 1:1, with about 3:4 preferred. While the preferred secondary solvent for the back-extraction is isopropyl ether, naphthas such as n-heptane, hexane, nonane, octane and the like can also be employed. The use of a naphtha will require higher proportions of back-extractant than will the ether, but it will also permit operation at higher temperatures.

In yet another embodiment of the invention, not illustrated in this flow sheet, the separation of the glycol from the uorene, dibenzofuran and acenaphthene is accomplished by distillation and Washing. Diethylene glycol will form azeotropes witl; i'luorene, dibenzofuran and acenaphthene which have boiling temperatures below the 245.8 C. boiling temperature of diethylene glycol. For example, the diethylene glycol-acenaphthene azeotropes has a boiling temperature of 239.6 C. and the diethylene glycol-fluorene azeotrope has a boiling temperature 0f 243 C. The three desired compounds would therefore be removed as azeotropes from which the glycol could then be water washed. Fractional distillation could then be employed to separate the three products.

While isopropanol is the preferred solvent for the recrystallization step employed for nal renement of the products, other solvents may also be employed. Suitable solvents include methanol, ethanol, isopropanol and other low molecular weight alcohols, as well as naphthas such as hexane, heptane and pentane. Relative purities of to 98 percent by weight can be obtained by the recrystallization of uorene, dibenzofuran and acenaphthene in this manner.

Example 1 Utilizing the procedure shown in the drawing, neutral middle oil feed containing 4.4 percent by weight of uorene was concurrently extracted with diethylene glycol and scrubbed with n-heptane in an 18 foot long mechanically agitated contactor column of 2-inch inside diameter. The volume ratio of oil to glycol to heptane was 1:24:5 and the temperature in the column was about 70 C. The glycol extract was back-extracted with isopropyl ether in an 18 foot long mechanically agitated contactor column of 2 inch inside diameter at ,a temperature of 50 C. The glycol extract was fed to the top of the extractor column and the ether was fed to the bottom of the column, the volume ratio of ether to glycol extract being 3:4. The ether extract thus formed was then washed with water after which the ether was distilled at a temperature of C. This .extracted product contained 74.8 percent of the iluorene originally present in the neutral middle oil. Fractional distillation was then employed to separate the product and after recrystallization from isopropanol iiuorence was obtained which was found to havea relative purity of 95 percent by Weight.

Example 2 Utilizing the procedure illustrated in the drawing, -neutral middle oil feed containing 21.5 percent by weight l of uorence, 3.9 percent by weight of acenaphthene and 2 percent by Weight of dibenzofuran was concurrently extracted with diethylene glycol and scrubbed with nheptane in an 18 foot long mechanically agitated contactor column of 2inch inside diameter. The Volume ratio of oil to glycol to heptane was 1:2425 and the temperature in the column was about 70 C. The glycol extract was back-extracted with isopropyl ether in an 18 foot long mechanically agitated contactor column of 2 inch inside diameter `at a temperature of 50 C. The glycol extract was yfed to the top of the agitated column and the ether was fed to the bottom of the column, the volume ratio of ether to glycol extract being 3:4. The ether extract thus formed was then Washed with water after which the ether Was distilled at a temperature ot', 110 C.

This extracted product contained 69.6 percent of the fluorene originally present in the middle oil and this extracted product was composed by Weight of 40.8

percent uorene, 18.1 percent dibenzofuran and 6.8 per- 20 What is claimed is:

The process for recovering liuorene, dibenzouran, and acenaphthene products from liquid coal hydrogenation neutral middle oil containing said products and at least one member of the group consisting of methylsubstituted fluorenes and naphthalene homologues, which process comprises extracting said products from-said oil with diethylene glycol and then extracting said products from the diethylene glycol extract with a secondary solvent selected from the group consisting of isopropyl ether and aliphatic hydrocarbons.

References Cited in the le of this patent UNITED STATES PATENTS 2,806,071 'Findlay sept. 1o, 1957 2,886,610 Georgian May 12, 1959 FOREIGN PATENTS 734,395 Great Britain Ju1y27, 195s OTHER REFERENCES Weissberger: Technique of Org., Chem;, vol. III (1950), p. 233. 

